A. Technical Field
The present invention relates to a production process for an ether carboxylate salt involving the use of a catalyst containing a rare earth element.
B. Background Art
A conventional production process for an ether carboxylate salt comprises the etherification step of reacting a hydroxyl-group-containing organic compound and a carboxyl-group-containing organic compound, wherein the carboxyl-group-containing organic compound is at least one compound selected from the group consisting of carboxyl-group-containing unsaturated organic compounds and carboxyl-group-containing epoxy compounds.
Sodium carboxymethoxysuccinate, which is one of the ether carboxylate salts, is useful as a phosphorus-free detergent builder and obtainable by a process comprising the step of reacting maleic anhydride and glycolic acid in an aqueous medium in the presence of calcium hydroxide (Chemical Abstract, 75, 89458 (1971)).
It is reported that the lanthanum (III) ion is also usable as the catalyst in place of the calcium ion in the same homogeneous reaction as above (Jeroen van Westrenen et al., J. Chem. Soc. Dalton Trans., 2723-2728 (1988)).
Processes involving the use of rare earth element ions such as lanthanum ion as the catalyst are more excellent in respect to higher activity of the catalyst, and further, higher selectivity and yield of the aimed product when compared with processes involving the use of the calcium ion.
However, the above conventional processes involving the use of rare earth element ions have problems as follows.
In those processes, a large amount of catalyst is used to smoothly run the reaction. However, the rare earth element is expensive, so it is desired to save the amount of the rare earth element, as used, or to recover and reuse the catalyst as already used for the reaction, for the purpose of saving the production cost.
The etherification reaction in a solution generally has problems in that: as the reaction advances, the concentration of raw compounds gradually lowers, so the reaction becomes difficult to advance, and the aimed ether compound therefore cannot be obtained with a high yield. The cause of such problems is that the ether compound, as once obtained, easily reverts to the raw compounds due to the reverse reaction, or that a side reaction competing with the reverse reaction occurs to give a by-product.